Dodecaphony pitch class

pitch.rb

class Pitch

  attr_reader :name

  VALID_PITCHES = {'A' => 0, 'B' => 2, 'C' => 3, 'D' => 5,
                   'E' => 7, 'F' => 8, 'G' => 10}

  SHARP_NAMES = {
    0 => 'A',
    1 => 'A#',
    2 => 'B',
    3 => 'C',
    4 => 'C#',
    5 => 'D',
    6 => 'D#',
    7 => 'E',
    8 => 'F',
    9 => 'F#',
    10 => 'G',
    11 => 'G#',
  }

  FLAT_NAMES = {
    0 => 'A',
    1 => 'Bb',
    2 => 'B',
    3 => 'C',
    4 => 'Db',
    5 => 'D',
    6 => 'Eb',
    7 => 'E',
    8 => 'F',
    9 => 'Gb',
    10 => 'G',
    11 => 'Ab',
  }


  private_constant :VALID_PITCHES

  def initialize pitch_name
    self.name = pitch_name
    validate_name
    self.pitch_number = adjust_for_accidentals(starting_number)
  end

  def distance_from second_pitch
    ensure_number_scale(second_pitch.pitch_number - pitch_number)
  end

  def spell_as_sharp
    SHARP_NAMES[pitch_number]
  end

  def spell_as_flat
    FLAT_NAMES[pitch_number]
  end

  protected

  attr_reader :pitch_number

  private

  attr_writer :name, :pitch_number

  def validate_name
    unless VALID_PITCHES.has_key?(starting_letter)
      raise ArgumentError, 'invalid pitch name'
    end
  end

  def accidentals
    name.downcase.split(//)[1..-1]
  end

  def adjust_for_accidentals number
    accidentals.each do |a|
      number += 1 if a == '+' or a == '#'
      number -= 1 if a == '-' or a == 'b'
    end
    ensure_number_scale number
  end

  def ensure_number_scale number
    number % 12
  end

  def starting_number
    VALID_PITCHES[starting_letter]
  end

  def starting_letter
    name.upcase.split(//)[0]
  end

end